In human patients, detection of toxins such as botulinum, from the bacterium Clostridium botulinum, has proven particularly difficult. Standard clinical methods now take from 48 hours to 10 days. For detection of botulinum toxin, we propose to test one of two versions of a novel point-of-care biosensor developed under a previous SBIR grant from NIH and recently patented (USPTO 6,103,535). Both prototypes respond in real time with high sensitivity. One device, for Phase I studies, relies on use of a tapered fiber and a fluorophore-based sandwich assay for detection. The other, for Phase II studies, uses a non-tapered, long-period Bragg grating, which does not require a sandwich assay or signal fluorophore, but rather generates a signal based on a change in the instrument's refractive index. Both systems can be used interchangeably with either proteins or nucleic acids. We further propose to prepare novel botulinum-sensitive devices by coupling antigenic single chain variable antibody (scFv's) to each biosensor surface. scFv's will be prepared by phage display and screened by bio-panning against the light chain of botulinum toxin type A. The use of small scFv's rather than large intact antibodies should further increase biosensor sensitivity and specificity. Each instrument configuration will be optimized for detection of botulinum toxin in human sera and compared for sensitivity, specificity, ease of operation, potential cost, and other factors. We will also compare each system to standard ELISA.